In hydraulic pumps which are driven by an electric motor, it has been common to provide an electric motor in one housing and the hydraulic pump in another housing with the two housings positioned in line so that the motor and pump have their own sets of bearings and shafts that are usually coupled through internal and external splines. Such an arrangement is axially long and necessitates the use of relatively expensive machined shafts and associated bearings. It has been suggested that the two housings utilize a common shaft but this makes the construction even more expensive since the shaft must be accurately formed. A typical such arrangement is shown in U.S. Pat. No. 3,672,793.
Among the objectives of the present invention are to provide an arrangement wherein the electric motor and pump are embodied in the same housing and coupled directly without a rotating shaft; which utilizes a simple stationary shaft that is readily made and yet maintains an accurate support for the rotating pump components; which is relatively simple, axially compact and rugged in construction; which is less costly to manufacture; which reduces the audible noise; which results in equal and opposite radial and axial forces on the yoke plate thereby reducing its stresses and the force on the supporting pintle bearings to a neglibile value; which results in smaller yoke spring and yoke control piston; which eliminates dynamic seals; which readily achieves a constant power operation without the aid of a compensator valve for this region; which automatically destrokes the yoke during starting should the pressure rise faster than the motor speed; which efficiently dissipates heat from the electric motor permitting the use of smaller and lighter motors capable of large overloads for short duration.
In accordance with the invention, an electric motor driven inline hydraulic pump comprises a common housing, a stationary shaft mounted in said housing and spaced pump cylinder block subassemblies that rotate around and are mounted on said shaft. Each subassembly includes a cylinder block and a plurality of circumferentially spaced pistons. The cylinder block subassemblies are positioned such that the pistons of one subassembly extend toward the other subassembly. A common yoke plate is mounted between the two cylinder blocks and bears the two groups of piston shoes, one on each of its two bearing surfaces. Each cylinder block is driven independent of and in direction opposite to the other by an electric motor integrally mounted such that its hollow rotor houses the block and drives it. All components described above are contained in one housing and operate submerged in hydraulic fluid.